The present invention relates to an improved plug valve structure and, more specifically, a plug valve structure where an improved seal is provided between the plug member and the valve body so that easier operation of the plug member in the valve body will be achieved while significant cost savings in the manufacture of the value will also be effected.
In the past, a variety of sealing structures for the well-known rotary plug valves for water and gas distribution systems have been developed. In view of the fact that the sealing elements of these valves and the valve elements themselves are subjected to wide ranges of fluid pressures as well as grit and dust that are frequently carried in the fluids being handled, certain limitations on the valve sealing elements have been encountered in designing these types of valve members. In one type of arrangement, it has been the practice to form the plug member of the valve with grooves which extend peripherally about the plug member fluid passage opening. Sealing elements such as O-rings would then be placed in the grooves. Such arrangements often required, for many applications, the provision of special lubrication to maintain the integrity of the seal over the life of the valve body. In addition, the machining of the groove has often been a significant manufacturing difficulty as well as a limitation on the design of the valve plug itself in terms of the shape and orientation of the fluid passageway therethrough. In particular, the machining of an oval groove in the plug body about the periphery of an opening therethrough has been both time consuming and expensive in terms of the labor and equipment required to carefully machine such a groove.
In other arrangements, where a machined groove has been employed to house a sealing element, certain applications have required a specially designed seal to resist degradation of the sealing effect as a result of exposure to grit and dirt in certain environments. This has materially increased the manufacturing costs of such valves.
In another technique, it has been the practice to cover the valve plug member with a resilient cover such as of molded rubber or other suitable elastomer such as that sold under the trademark Neoprene. Alternately, the valve body chamber in which the plug was to be inserted, in some arrangements, has been coated with the resilient material. In either case, the sealing effect depended largely on the exact manufacturing tolerances as between the outer diameter of the plug member and the facing wall of the plug receiving chamber of the valve body. The maintenance of such close tolerances as were required to assure proper operation of the valve over its useful life materially increases the manufacturing costs on the one hand, and, on the other, with such valve structures, it was difficult to compensate for differential expansion as between the valve elements themselves and the resilient material covering that was employed. Further, operation of the valve could often be materially impeded by uneven wear on the resilient cover particularly where the fluid being handled carried any significant quantity of grit and dirt. In addition, where any pressure fluids were involved, in order to minimize the effect of cold flow of the rubber covering, a false port often had to be provided on the face of the plug member to absorb any bulge or distortion caused by a long term shut-off of the valve. In addition a false port is useful to prevent grit and dust from adhering to the seating surfaces which could result in damage to the seating surfaces upon rotation of the valve between its operating positions. A false port, in this case, is provided by forming a recess in the covering material and/or in the plug member itself to reduce seating contact and to thereby render turning of the plug member in the valve body easier.
In both of the foregoing alternatives, a plug member could only be provided with a single flow passage since it was essentially uneconomical to machine a separate flow passage in the valve body and provide alternate valve plug structures so that a user could accommodate alternate flow passages thus provided in the valve body.
The present invention provides a rotary plug valve structure which avoids the foregoing difficulties and provides a superior seal for a rotary plug valve which is less expensive to manufacture and yet which is capable of accommodating alternate plug valve bodies having different flow paths.
In one embodiment, the valve body which has a cylindrical internal plug receiving chamber is provided with a pattern of raised ridges only the inner surfaces of which need be machined to close tolerances. The alternate valve bodies may be used which have a different flow paths so that the plug member may be employed by the user with a selected valve body to suit the circumstances of a particular installation. The plug member itself is cylindrically shaped and, in one embodiment has a longitudinal axis and a fluid passage extending therethrough perpendicular to the longitudinal axis. The external surface of the plug member is provided with a resilient covering such as of rubber or other suitable resilient elastomer to an extent such that the cover will overlie the entire pattern of ridges provided on the interior wall of the valve body. The depth of the resilient cover is selected such that when a portion of the resilient cover engages a ridge of the valve body, the cover will be compressed sufficiently to effect the desired sealing to prevent fluid leakage between the cover and the contacting ridge.
With this structure, much less machining or grinding is required in manufacturing the valve body and plug than has heretofore been the case. In addition, deterioration of the resilient cover as a result of the presence of grit or dirt in the fluid being handled will be significantly reduced as a result of the reduced contact of the resilient cover over its surface with the raised ridges as well as the type of movement involved in opening and closing the valve passages.
The foregoing and other advantages will become apparent as consideration is given to the following detailed description taken in conjunction with the accompanying drawings, in which: